Rotary grass cutters, edgers and trimmers are long known in the art using both flexible cord and rigid steel cutting members. It is convenient and inexpensive to use common steel nails for cutting blades as evidenced by the following U.S. Patents:
In U.S. Pat. No. 2,888,993 for Lawn Edger, Jun. 2, 1959, M. W. Dunning inserts a set of six nails into apertures of a rubber ring clamped between a pair of metal disks upon a rotary drive shaft. This has the deficiencies of heavy weight metal construction and the rapid deterioration and wear of rubber under encountered cutting conditions, particularly when vegetation heavier than ordinary lawn grass is to be cut thus introducing high stresses.
In U.S. Pat. Nos. 3,684,027 and 3,684,028 for Grass Edger, Aug. 15, 1972 and U.S. Pat. No. 3,900,071 for Plate Type Nail Holder for Edgers, Trimmers, or Other Applications, Aug. 19, 1975, H. H. Crawford disposes three nails with heads individually arranged and nested in open ended hollow steel cylindrical bosses located on a rotatable plate to be retained in place by a spring biased metal cover plate. Not only is this head heavy but particularly under the stresses of heavy industrial cutting the spring biassed retention plate is subject to chatter and malfunction with loss of and damage to the nail cutter arms.
Such prior art further has the disadvantage of wear and tear and catastrophic damage that is particularly encountered with the use of inflexibly held nail cutter arms that could encounter boards, sidewalk edges and the like in use causing enough damage to expensive head construction features that the heads must be replaced frequently.
Furthermore these rotary heads are not adapted for general purpose use of a single mower head for both ordinary grass that is relatively tender and heavier vegetation including weed stems. For example, flexible cord, typically plastic, is not effective for cutting the heavier vegetation. And furthermore the weight of the nails and rigid steel mounting structure is great enough to limit rotor speed at a given power, thus reducing cutting efficiency.
In general therefore, the prior art has failed to correct the aforesaid deficiencies and has not produced a versatile, lightweight, low-cost, long-lasting, high-speed cutter head that rapidly covers large cutting areas to provide improved performance in the presence of both grass and heavier vegetation.
It is accordingly an objective of this invention to provide an improved rotary cutter head that corrects the foregoing problems of the prior art. Other objectives, features and advantages of this invention will be found throughout the following description, claims and the accompanying drawings.